1. Field of the Invention
This invention relates generally to semiconductor device manufacturing, and more particularly, to wire bonding machines.
2. Description of the Prior Art
In manufacturing a semiconductor device, such as an semiconductor device 110 as illustrated in FIG. 1A, packaging is often required so that the signals can be bidirectionally communicated between the semiconductor device and other electronic devices. Semiconductor device 110 includes a semiconductor die or substrate 112 inserted or molded into a package 114 so that the semiconductor device may be installed onto a printed circuit board (not illustrated). The package 114 further provides a metal leadframe 116 so that electrical signals may be communicated between the semiconductor die 112 and the printed circuit board and other integrated circuits 110 or electronic components.
Referring to FIG. 1A, the semiconductor device 110 includes the dual inline pin package 114, the semiconductor die 112, the metal leadframe 116, a molded compound shell 118, and bond wires 120. The bond wires 120 are made of a conducting material, preferably gold or aluminum, and couple to the semiconductor die 112 at one end and the leadframe 116 at the opposite end. The traces of the lead frame that couple to the printed circuit board are often referred to as pins 122.
In the semiconductor device manufacturing process a wire bonding machine (not illustrated in FIG. 1A) couples the bond wires 120 to the semiconductor die 112 and the leadframe 116. Referring to FIG. 1B, a bonding tool 124 of the wire bonding machine generates a ball bond 126 between the bond wire 120 and the semiconductor die 112. The bonding tool 124 is coupled to a bonding head (not illustrated in FIG. 1B) of the wire bonding machine. Referring to FIG. 1C, the bonding tool 124 has completed a wedge bond 128 between the bond wire 120 and the leadframe 116.
Generally thermosonic bonding techniques of bonding may be used to generate the ball bond 126. Thermosonic bonding utilizes a heat source to heat one end of the bond wire 120 to generate a ball and simultaneously applies a vertical load to the ball while ultrasonically exciting the bond wire 120. Generally ultrasonic bonding techniques are used to generate the wedge bond 128. In generating the wedge bond, the bond wire 120 is first wedged between the leadframe 116 or other bonding surface and the bonding tool 124 as illustrated in FIG. 1B. While the bond wire 120 is under a vertical load, a mechanical motion or pulsing of the bonding tool 124 generates an ultrasonic wave motion generating sufficient energy to heat the end of the bond wire 120 breaking surface oxides on the bonding surface and at the end of the bond wire so that the new surfaces may cold-weld together. Proper loading and ultrasonic wave motion must occur for the wedge bond 128 to be properly formed.
The bonding of the bond wire 120 in FIG. 1C is referred to as ball-wedge bonding. In the case where a wedge bond 128 is formed at both ends of the bond wire 120, it is referred to as wedge-wedge bonding. FIG. 1D illustrates wedge-wedge bonding of the bond wire 120. A wedge bond 128 is formed at the end of the bond wire 120 attached to the semiconductor die 112 and a second wedge bond 128 is formed at the end of the bond wire 120 attached to the leadframe 116. Wedge-wedge bonding may be preferable such that thermosonic bonding techniques of ball bonding may be avoided. In ball-wedge bonding the bonding tool 124 may be a capillary device. In wedge-wedge bonding the bonding tool 124 may be a wedge device.
Referring to FIG. 1E, the semiconductor device 110 includes the semiconductor die 112 and the leadframe 116. FIG. 1E illustrates ball-wedge bonding. The semiconductor die 112 includes bonding pads 130 so that the bonding wires 120 may be attached thereto using ball bonds 126. The surface of the bonding pads 130 are made of a conductive material which is preferably aluminum metal. The leadframe 116 includes contact points 132 such that the bonding wires 120 may be attached thereto using wedge bonds 128. FIG. 1F illustrates wedge-wedge bonding. The bonding wires 120 are attached to the bonding pads 130 of the semiconductor die 112 using wedge bonds 128. The bonding wires 120 are attached to the contact points 132 of the lead frame 116 using wedge bonds 128.
In order to bond to all bonding pads 130 of the semiconductor die 112 and to all the contact points 132 on the leadframe 116, the bonding tool 124 must be properly positioned. Previously the proper position of the bonding tool was accomplished by physically moving the bonding tool 124 itself from one point to another point while the semiconductor device remained fixed, physically moving the semiconductor device 110 while the bonding tool 124 remained fixed, or moving both the bonding tool 124 and the semiconductor device 110. Furthermore in wedge-wedge bonding, the bond wire connection path must be aligned with the wire feeding direction of the bonding tool.
Previously automatic wedge wire bonders provided four axis of motion namely X, Y, Z, and .theta. (theta) to perform wire bonding. The X and Y axis movements position the semiconductor bonding pads 130 of the semiconductor die 112 under the bonding tool 124 or position the contact points 132 of the leadframe 116 to be under the bonding tool 124. Traditionally, the X and Y axis movements further define the locus of the wire path from the bonding pad 130 to the contact point 132. The .theta. rotational axis of movement aligns the wire feed direction of the bonding tool 124 with the wire path. Referring to FIG. 1C, the Z vertical axis of movement provides that the bonding tool 124 with its wedge makes contact with the bond wire 120 which in turn makes contact with the bonding pads 130 or contact points 132 such that the welding process may occur.
In order to perform the wire bonding process previous wire bonders may move the semiconductor device 110 or the bonding head coupled to the bonding tool 124 in various ways. In one case the semiconductor device 110 is moved in the X, Y, and .theta. axis while the bonding head and bonding tool 124 are moved only in the Z axis. In another case the semiconductor device 110 is moved in the X and Y axis while the bonding head and bonding tool 124 are moved in the .theta. axis and the Z axis. In another case the semiconductor device 110 is moved only in the .theta. axis while the bonding head and bonding tool 124 are moved in the X, Y, and Z axis. In another case the semiconductor device 110 is moved only in the Z axis while the bonding head and bonding tool 124 are moved in the X, Y, and .theta. axis. In another case the semiconductor device 110 is moved in the Z and .theta. axis while the bonding head and bonding tool 124 are moved in the X and Y axis. In another case the semiconductor device 110 is stationary during the bonding process while the bonding head and bonding tool 124 are moved in the X, Y, .theta., and Z axis.
In order to increase the efficiency of the wire bonding process, it is desirable to handle the semiconductor devices using an automatic continuous indexing technique. Automatic continuous indexing is a technique where an index mark on the semiconductor device 110 or a device carrier (not illustrated) is used to automatically align a bonding start point as the next semiconductor device is inserted into the wire bonder for bonding. Wire bonding machines that move the semiconductor device 110 in order to position it under the bonding tool 124, can hardly use an automatic continuous index handling method. It is desirable to provide automatic continuous index handling such that the semiconductor devices 110 are stationary during the bonding process.
Semiconductor devices 110 of today may be much larger and may require a large number of pins 122 in order to communicate properly with a printed circuit board. These large devices have a relatively large mass and generally require a heavy workholder clamp in order to hold the semiconductor device 110 in the bonding machine. In wire bonders such as these where the semiconductor device 110 is moved, the large mass of the workholder clamp and the large semiconductor devices 110 result in poor dynamic stability and vibrations during a high speed bonding process. A prior technique used to combat the vibration problems in wire bonders reduces the bonding speed such that proper dynamic stability may be achieved. However, it is desirable to operate wire bonding machines at their maximum bonding speed when bonding large devices. It is also desirable to keep the semiconductor device 110 stationary during the wire bonding process.
In wire bonders where the semiconductor device 110 is stationary while the bonding head and bonding tool 124 are moved in the X, Y, .theta., and Z axis, the bonding head is rather complicated and has a relatively large mass. The large mass of the bonding head makes it difficult to achieve good dynamic stability. This is particularly a problem when the bonding head and bonding tool 124 move in the X and Y axis directions from the semiconductor device bonding pad 130 to the contact points 132 as illustrated by the arrow 142 in FIG. 1E and FIG. 1F. A prior technique used to provide proper dynamic stability is to reduce the speed of the bonding process. However, it is desirable to speed up the bonding process of semiconductor devices in order to increase the throughput and thereby lowering manufacturing costs.
In the wire bonding process it is desirable to occasionally view the progress of the wire bonder in order to maintain quality controls. Traditionally a microscope (not illustrated) is used to visualize the real time wire-bonding process. The microscope may be coupled to the bonder and aligned such that its lens points to the device to allow visual inspection of the top surface of semiconductor die 112 and leadframe 116. In wire bonders where the bonding head and bonding tool 124 move and rotate in various directions it is difficult if not impossible to properly view the wire bonding process. However, it is desirable to properly view the bonding process in the case where the bonding head and bonding tool 124 move in order to complete the bonding process.